From 6406766e5a175c87dfc20c1ff1374c8c8a163517 Mon Sep 17 00:00:00 2001
From: Matthew Hall <hallmatthew314@gmail.com>
Date: Sat, 18 Mar 2023 22:47:02 +1300
Subject: Many and Some

---
 spec/parcom_spec.cr  | 35 +++++++++++++++++++++++++++++++++++
 src/parcom/parser.cr | 23 +++++++++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/spec/parcom_spec.cr b/spec/parcom_spec.cr
index 86ad93a..870b0a2 100644
--- a/spec/parcom_spec.cr
+++ b/spec/parcom_spec.cr
@@ -380,5 +380,40 @@ describe Parser do
       result.value.should eq('b')
     end
   end
+
+  describe "#many" do
+    p = Parser(Char, Char).token('a').many
+
+    it "returns no results if it never succeeds" do
+      ["", "bb"].each do |s|
+        tokens = Tokens.from_string(s)
+        result = p.parse(tokens)
+
+        result.value.empty?.should be_true
+        result.tokens.should eq(tokens)
+      end
+    end
+
+    it "parses as many times as possible" do
+      ["a", "aaa", "aaaaa"].each do |s|
+        tokens = Tokens.from_string(s)
+        result = p.parse(tokens)
+
+        result.value.should eq(s.chars)
+        result.tokens.empty?.should be_true
+      end
+    end
+  end
+
+  describe "#some" do
+    p = Parser(Char, Char).token('a').some
+
+    it "fails if it cannot parse at least once" do
+      ["", "bb"].each do |s|
+        tokens = Tokens.from_string(s)
+        expect_raises(ParserFail) { p.parse(tokens) }
+      end
+    end
+  end
 end
 
diff --git a/src/parcom/parser.cr b/src/parcom/parser.cr
index fcfe292..8ee3f68 100644
--- a/src/parcom/parser.cr
+++ b/src/parcom/parser.cr
@@ -241,6 +241,29 @@ module Parcom
       p1 = self
       (p1 + p2).map(&.last).named("#{p1.name} >> #{p2.name}")
     end
+
+    # Creates a new parser from `self` that parses with `self` as many times
+    # as possible. If it never succeeds, returns an empty list.
+    def many : Parser(T, Array(U))
+      p = self
+      Parser(T, Array(U)).new("Many: #{p.name}") do |tokens|
+        values = [] of U
+        r = p.parse?(tokens)
+        until r.nil?
+          break unless tokens != r.tokens
+          tokens = r.tokens
+          values << r.value
+          r = p.parse?(tokens)
+        end
+        Result.new(tokens, values)
+      end
+    end
+
+    # Creates a new parser from `self` that parses with `self` as many times
+    # as possible. Raises `ParserFail` it never succeeds.
+    def some : Parser(T, Array(U))
+      many.assert { |arr| !arr.empty? }.named("Some: #{@name}")
+    end
   end
 end
 
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